This invention is directed to screwdrivers and more particularly to expandable bit screw holding screwdrivers.
Various types of expandable bit screw holding screwdrivers have been proposed by the prior art. In the past, these screwdrivers have had various disadvantages, many of which are overcome by the screwdriver described in U.S. Pat. No. 3,900,057. As noted above, U.S. Pat. No. 3,900,057 is primarily directed to a new and improved blade configuration. While this blade configuration has a variety of advantages over prior art blade configurations, the slide mechanism proposed for use in that screwdriver has certain disadvantages, particularly when the overall structure is embodied in a relatively large screwdriver. This invention is primarily directed to overcoming the disadvantages of that slide mechanism.
More specifically, the slide mechanism disclosed in U.S. Pat. No. 3,900,057 is similar to the slide mechanism disclosed in U.S. Pat. No. 3,224,479 and comprises a cylindrical member surrounding a split shank or shaft formed of two pieces that diverge outwardly, at least in the region of the blade. As the cylindrical member (slide) is moved from the screwdriver handle end of the shank toward the blade end, the diverging tips are forced toward one another causing the blade to expand in thickness. This slide mechanism has a number of disadvantages. First, as the diverging portions of the blade are forced toward one another, the portions of the split shank located inside of the slide tend to diverge, i.e., the two shank elements move away from one another, weakening the shank. In this regard attention is directed to FIG. 3 of U.S. Pat. No. 3,224,479. Second, the blade element maximum divergence is determined by the spring action of the split shanks, not by any external mechanical force. Third, the tight engagement of the blade in a screw slot may not be effectively released when a slide of this nature is withdrawn toward the handle because the slide does not create a releasing force. Rather, release force depends upon the spring force developed by the split shank.
While the present invention is primarily suited for use with an expandable bit screw holding screwdriver of the type described in U.S. Pat. No. 3,900,057, it readily will be recognized that it is also useful with other types of expandable bit screw holding screwdrivers, and other devices. p It is an object of this invention to provide a new and improved expandable bit screw holding screwdriver.
It is a further object of this invention to provide a slide mechanism suitable for use in controlling the expansion of a split shank such as that employed in an expandable bit screw holding screwdriver.
It is yet another object of this invention to provide a new and improved slide mechanism for an expandable bit screw holding screwdriver that creates a mechanical force that acts to expand and contract shank elements to thicken and thin the screwdriver blade formed by the tips of the shank elements, as desired.
Another disadvantage of prior art expandable bit screw holding screwdrivers relates to the configuration of the tip of the blade. Specifically, in most cases, as with conventional screwdrivers, the periphery of the tip of the blade of such a screwdriver lies orthogonal to the longitudinal axis of the shank. A "flat" blade tip periphery of this nature has certain disadvantages. For example, if a screw slot is occluded, the blade will not readily grip the sides of the screw slot. This invention is also directed to overcoming this disadvantage.
Therefore, it is a still further object of this invention to provide a new and improved blade tip configuration for an expandable bit screw holding screwdriver.
It is yet another object of this invention to provide a new and improved expandable bit screw holding screwdriver having a blade tip configuration adapted to more readily engage screw slots, particularly those wherein a portion of the slot is occluded.